This invention concerns processes, apparatuses and systems for producing powder of extremely small, highly uniform spherical shape, having high sphericity, and composed of metal including single metals and alloys, including nano-composite structures, using a self-assembling procedure. The present invention further includes the powder particles produced by the processes, apparatuses and systems of the present invention. The powder particles may be used for example, as the starting materials of magnets, catalysts, electrodes, batteries, heat insulators, refractory materials, and sintered metals. For instance, the powders of the rare earth-iron-boron ( Rxe2x80x94Fexe2x80x94B) alloy with the nanocomposite structure of the present invention may be used a starting material for producing a sintered magnet or bonded magnet having excellent magnetic characteristics
Various kinds of the powders of metals, metal oxides, metal nitrides, metal silicides, and their mixed compounds have been used as the crude starting materials to produce such materials as magnets, catalysts, electrodes, batteries, heat insulators, refractory substances, and sintered metals. Such powders commonly suffer from poor uniformity of composition, shape, granularity and for spherical powders, poor sphericity (degree of roundness). A mechanical pulverization apparatus is capable of producing particles that have fine structure and are composed of more than two types of components. While of possibly uniform composition, such particles are of poor uniformity in size and shape, and of course are not of spherical shape. Moreover, it is difficult to obtain a nanocomposite structure using mechanical pulverization for the production of fine powders.
The apparatuses, systems and self assembling processes of the present invention provides for the production of very small, spherical particles having a nano-composite structure which is a particularly important embodiment of the present invention having high utility as strong permanent magnetic powders. Conventional apparatuses and methods can not result in a nanocomposite magnetic material at all, and certainly not result in the present tiny spherical powders by a self-assembly technique.
For example, materials for permanent magnet are disclosed for example in Japanese patent publication Hei 7-78269 (Japanese patent application Sho 58-94876, the patent families include U.S. Pat. Nos. 4,770,723; 4,792,368; 4,840,684; 5,096,512; 5,183,516; 5,194,098; 5,466,308; 5,645,651), which discloses (a) RFeB compounds containing R (at least one kind of rare earth element including Y), Fe and B as essential elements and having a tetragonal crystal structure with lattice constants of a0 about 9 xc3x85 and c0 about 12 xc3x85, and each compound is isolated by non-magnetic phase, and (b) RFeBA compounds containing R, Fe, B and A (A=Ti, Ni, Bi, V, Nb, Ta, Cr, Mo, W, Mn, Al, Sb, Ge, Sn, Zr, Hf, Cu, S, C, Ca, Mg, Si, O, or P) as essential elements and having a tetragonal crystal structure with lattice constants of a0, about 9 xc3x85 and c0 about 12 xc3x85, and each compound is isolated by non-magnetic phase. Though this magnet shows excellent magnetic properties, the latent ability of the RFeB or RFeBA tetragonal compounds have not been exhibited fully.
U.S. Pat. No. 5,942,053 provides a composition for permanent magnet that employs a RFeB system tetragonal tetragonal compounds. This magnet is a complex of (1) a crystalline RFeB or RFeCoB compounds having a tetragonal crystal structure with lattice constants of a0 about 8.8 xc3x85 and c0 about 12 xc3x85, in which R is at least one of rare earth elements, and (2) a crystalline neodymium oxide having a cubic crystal structure, wherein both crystal grains of (1) and (2) are epitaxially connected and the RFeB or RFeCoB crystal grains are oriented to the c0 direction. While the resulting magnet has very good magnetic properties, no effort was made to control the nanostructure of the composition and thus the U.S. Pat. No. ""053 magnet does not employ the nano-sized and non-magnetic material, neodymium oxide that is incorporated at the inside of the NdFeB ferromagnetic grains and/or at their grain boundaries as in the present invention. The U.S. Pat. No. ""053 magnet does not employ the nanostructure consisting of micro-sized ferromagnetic phase and nano-sized nonmagnetic phase resulting in the nanocomposite structure of the present invention.
Conventional apparatuses for producing metal spheres include means for melting the metal and pouring the metal upon a rotating base that flings the molten metal to form spheroid particles. See JP 51-64456, JP 07-179912, JP 63-33508 and JP 07-173510. Such typical atomization apparatuses produce spherical powders having poor sphericity, limited microdimensions and poor uniformity of composition and shape. The methods and apparatuses of the present invention provide for producing particles of extremely small, highly uniform spherical shape, further providing for particles having nanocomposite structures by self-assembly of such structure.
This invention provides methods, apparatuses and systems for producing powder particles of extremely small, highly uniform spherical shape and high sphericity, composed of metal including single metals and alloys, including nanocomposite structures, using a self-assembling procedure. The invention further includes the produced powder particles.
The nanocomposite structures provide for a permanent magnet with excellent magnetic properties employing nano-sized, non-magnetic material, which is a rare earth oxide, ROx, R2O3, RO, RO2, such as neodymium oxide or praseodymium oxide, (or MOx where M is a minor metal as exemplified below) that is incorporated at the inside of ferromagnetic grains, such as Rxe2x80x94Fexe2x80x94B, and/or at their grain boundaries. Usually, Nd is preferably employed as R, and rare earth elements such as Pr is favorably employed. Nd2O3, RO and RO2 are preferably used in the present invention. The resulting novel nanostructure consists of micro-sized ferromagnetic phase and novel nano-sized nonmagnetic phase providing for the overall novel nanocomposite structure of the present invention.
More generally, the nanocomposite metal particles in the present invention is the aggregate of nano-sized metal components separated within the particles by layers or discrete nano-sized bodies of metal oxides, metal nitrides, metal suicides, or separated by evacuated spaces, e.g. pores.
Additionally, the methods, apparatuses and systems of the present invention for produce powder of extremely small, highly uniform spherical shape and high sphericity, composed of substantially amorphous or crystalline (e.g., nanocomposites) composition, and by control of process parameters, having controlled porosity.
Thus, the products of the present invention are particles being 1) substantially crystalline; 2) substantially amorphous; or 3) of controlled porosity. The metal powders are produced by methods, apparatuses and systems wherein molten metal, alloys or composites are dropped onto a fast-rotating dish shaped disk in an atmosphere containing one or more inert gases and a small amount of oxidizing gas, and the molten metal is dispersed to be tiny droplets for a predetermined time using centrifugal force, within a cooling-reaction gas, and cooled rapidly to form spherical particles.